The measurement and characterization of gait (i.e. human or animal) is performed by a wide range of methods. At one end of the scale is the measurement and analysis possibilities found in a well equipped bio-mechanical lab. The equipment in these labs typically includes automated 3D optical measurement systems, force plates and physiological output indicators. The output from these transducers are fed into a central computer that enables a wide range of analysis and display possibilities. At the other end of the spectrum is the simplified analysis performed with a ruler, stopwatch and trained clinical observations.
The reasons determining gait kinematic properties (such as acceleration, velocity and position) range from: (i) personal interest, (ii) training and performance considerations of the serious athlete, (iii) rehabilitation of the disabled or (iv) for the design and analysis of footwear.
From an athletic point of view, runners, joggers and walkers often like to know how far they have journeyed and how fast they have traveled, but have had only limited cumbersome ways to measure distance and speed. Distance can be measured after the fact with a calibrated bicycle or automobile or by traveling on a known premeasured route. For determining one's speed, a simple approach is to travel a known, fixed distance on a track or road and then record the length of time required to cover the distance. This method suffers from several limitations including (i) limited walking/running routes, (ii) speed indication at measured intervals only and (iii) only an average velocity is determined over the given distance.
There are a number of portable pedometers that attempt to tackle the problem of measuring both distance and velocity. However, they have failed to gain wide spread use, because these devices are essentially limited to stride counting. Distance and speed can only be estimated if stride length consistency is assumed. This approach is inaccurate because an individual's stride length changes considerably from day to day or even within one session due to changes in terrain, fatigue, interval training, or other factors.
U.S. Pat. No. 3,355,942 discloses a pedometer that counts strides based on compression cycles in a bellows under the heel and then estimates distance based on average stride length. The invention described in U.S. Pat. No. 4,741,001 uses a spirit-biased pendulum to count strides. The pedometer disclosed in U.S. Pat. No. 4,649,552 uses a step sensor sealed into an insole to count strides. The pedometer of U.S. Pat. No. 4,651,446 counts strides by detecting flexion of the instep. Other counting pedometers include those under U.S. Pat. Nos. 5,117,444, 5,065,414, 4,855,942, 4,510,704, 4,460,823, 4,371,945, 4,322,609, 4,053,755, 3,818,194 and 3,635,399.
The majority of the patented pedometers are simply different methods of stride counting and do not address the problem of varying stride length. However, a pedometer listed under U.S. Pat. No. 4,371,945 uses ultrasonic emitters and sensors on alternate legs to measure the maximum distance between legs during each stride. While this is a significant improvement, this is only suitable for simple, low-speed gait patterns (no flight stage) and requires two sets of transducers; one on each leg.
The broad concept of using accelerometers for determining the velocity and distance traveled, for example by athletes, is described in German Patent 4,222,373. This patent describes the use of an accelerometer and integration to determine velocity and route or position. This device apparently processes acceleration data continuously and thus has an accumulated error from drift so that in very short period of time, the resulting data contains significant inaccuracies. The inventor indicates that this device is useful for skiers, surfers, sailors, cyclists, etc. and thus is not related to a striding device or for measuring the kinematics of striding and would not be effective for that purpose.
The Russian Patents 862074 and 885879 both by Volkov describe the attempts to overcome accumulated error in acceleration measuring devices by using a bar generator in combination with a summator and integrator. This described device does not make use of updated reference points and is thus also prone to accumulated drift.
A paper entitled "Estimation of Speed and Inclination of Walking Using Neural Networks" by Aminian et al., Published in the IEEE, Transactions on Instrumentations and Measurements; Volume 44 #3, June 1995, describes a portable data logger designed to record body accelerations during walking and uses three orthogonal accelerometers placed on the waistbelt to measure forward, vertical and heel acceleration. By means of neural networks, it correlates the recorded signals to the desired gait velocity and angle of incline. The generality of this method is questionable and no other gait information is produced.